1. Field of the Invention
The present invention relates generally to a biodegradable and hydrolyzable resin composition having good physical properties such as tensile strength. More specifically, the present invention relates to a resin composition obtained by blending a thermoplastic aliphatic polyester resin and a polyester urethane. The present resin composition has widespread applications such as wastebag films and food packaging films.
2. Description of the Related Arts
Generally, synthetic resins have been used in daily lives because of good mechanical properties, chemical resistance, durability and so on. However, because these resins are not biodegradable, the wastes of used resins cause a serious environmental pollution. Therefore, there has been a need for biodegradable resins that can substitute for synthetic resins, and various research has been made to develop them.
However, the obtained resins having 100% of biodegradation exhibit very weak strength not suitable for wastebags or packaging films. Therefore, there has been need for new resins having both biodegradability and improved strength.
As a biodegradable resin, aliphatic polyester has been used (Journal of Macromol SCi-Chem., A-23(3), 1986, 393-409). But, because of their main chain structure and crystalline characters, the above aliphatic polyester has a low melting point and a high melt flow index exhibiting poor heat resistance and physical properties such as mechanical strength.
To improve these properties of aliphatic polyesters, Japanese Laid-open Patents (Laid-open Publication No. 4-189822 and No. 4-189823) proposed a method for increasing molecular weight of aliphatic polyester by reacting aliphatic dicarboxylic acid with glycol to obtain aliphatic polyester with about 15,000 of number average molecular weight (hereinafter referred to as Mn), then crosslinking the aliphatic polyester with diisocynate. However, while preparing of low-molecular-weight aliphatic polyester with this method, undesirable microgel particles are formed and deteriorate the quality. Besides, because the diisocynate crosslinks with aliphatic polyester in a short time, unreacted diisocynates exist in products and become a new factor of pollution.
Accordingly, in order to solve the conventional problems and to improve the physical properties of biodegradable resins, the present inventors have researched repeatedly to find that resin compositions obtained by blending biodegradable aliphatic polyester resin with hydrolyzable polyester urethane having good processing property and high molecular weight, exhibit good physical and molding properties as well as good biodegradability and hydrolyzability.